This invention relates in general to gas operated firearms and deals more particularly with an improved gas actuated operating mechanism for a semiautomatic firearm. The operating mechanism of the present invention is particularly adapted for use in an autoloaded shotgun of the type wherein gases of explosion, developed on discharge of the firearm, are bled from the gun bore to a gas cylinder to react upon a piston which exerts impelling force upon an inertia weight comprising part of the mechanism. The inertia weight, connected to a bolt assembly through an action bar, provides initial impetus to unlock the bolt and urge it from its battery position toward a retired position, whereupon the spent shell is extracted and ejected, the trigger mechanism is cocked, and a spring for returning the bolt assembly to battery is compressed. Shotguns having gas actuated operating mechanisms of the aforedescribed general type are illustrated and described in U.S. Pat. No. 2,909,101 to Hillberg, assigned to High Standard Manufacturing Corporation, et al; U.S. Pat. No. 3,200,710 to Kelly et al, assigned to Remington Arms Company, Inc.; and U.S. Pat. No. 3,580,132 to Vartanian, assigned to Olin Mathieson Chemical Corporation.
In a firearm of the aforedescribed general type, such as the one shown in the aforementioned patent to Hillberg, for example, wherein the bolt assembly and the various parts of the operating mechanism for moving it are secured in fixed relation to each other and move as a unit, all of the parts which comprise the unit impact simultaneously. This impact must be absorbed by the receiver. In addition to adding substantially to recoil, the various parts of the mechanism are subjected to substantial stress, requiring that the parts be heavier in section and of higher material strength than might otherwise be required, all of which adds substantially to the weight of the gun.
This problem has been overcome, to some degree, by providing for travel allowance between the various parts of the mechanism, taught by Vartanian. Firearms have heretofore been provided wherein such travel allowances enable the bolt assembly, the action bar, and the inertia weight to impact separately and at different times during an operating cycle whereby the total impact of the mechanism is divided and occurs in stages as three separate and distinct impacts.
In mechanisms of the aforedescribed general type the action bar often serves to block a bolt locking member in locking position when the bolt assembly is in battery. In such a mechanism, it is generally desirable that the action bar be positively retained in fixed position relative to the bolt assembly, or more specifically the bolt locking element associated therewith, whereby to assure positive retention of the locking element in locked position when the bolt assembly is in battery. However, the aforediscussed requirement for travel allowance between various parts of the mechanism has made it difficult to produce a satisfactory system which fully meets this objective.
In the aforementioned patent to Vartanian, for example, an auxiliary spring is provided which acts between an action bar and an inertia weight to maintain the latter elements in abutting contact when the bolt assembly is in battery position. While such an arrangement may be useful to eliminate free play or looseness between parts of a system, is not particularly satisfactory for maintaining an action bar in blocking position relative to a bolt locking element, because it lacks the requisite fail-safe feature essential to such a mechanism. Should the auxiliary spring be broken or damaged, the action bar could move from its blocking position relative to the bolt locking element, while the gun remains otherwise operative.
Accordingly, it is the general aim of the present invention to provide an improved gas actuated bolt operating mechanism of the aforedescribed general type which provides for further division of impact load, while assuring positive bolt lock-up in battery position.